ABSTRACT Negative symptoms such as avolition, blunted affect, anhedonia, and social withdrawal, are debilitating, persistent, and significantly contribute to the huge personal and economic cost of severe psychiatric illnesses. In recent onset (RO) patients, negative symptoms are associated with poor functional outcomes. In individuals at clinical high-risk (CHR) for psychosis, negative symptoms can predict transition, and are also associated with poor and deteriorating functioning. This is particularly significant because even though most CHR individuals do not transition to psychosis, they nonetheless exhibit substantial impairments in social and occupational functioning that considerably impact quality of life. Negative symptoms are largely unaddressed by medications. Proline is a precursor of the neurotransmitter glutamate and functions as a CNS neuromodulator. Catechol-O- methyltransferase (COMT) deactivates catecholamines including dopamine (DA). We recently found an interaction between fasting plasma proline and a functional COMT polymorphism (shown to modulate DA signaling via COMT enzyme activity:DA metabolism), significantly predicts negative symptom outcomes in chronic psychiatric patients: In patients? predicted to have high COMT activity (and enhanced DA metabolism), high proline is protective with low negative symptom severity or a greater symptom reduction over time. Conversely, carriers of the allele encoding the low activity enzyme demonstrated significantly more negative symptoms with high proline. This negative symptom interaction effect was consistent across two psychiatric illnesses. We now hypothesize that proline level and DA metabolism (as measured by COMT activity) interact to modify negative symptom severity in CHR individuals and in those with RO. We further hypothesize a significant relationship between proline, DA metabolism, and change in negative symptoms in CHR states, as well as conversion to psychosis. Specific Aims. Aim 1A. To collect cross-sectional, fasting blood from 67 CHR individuals and 69 RO patients (<2 years from their first-episode), and measure fasting plasma proline levels plus erythrocyte COMT enzyme activity. Aim 1B. To evaluate negative symptoms and functional outcomes in the two groups using a battery of instruments including the Scale for Assessment of Negative Symptoms (SANS), and test for an interaction between DA metabolism and proline. Aim 2. To longitudinally examine the change in fasting plasma proline and negative symptoms (as assessed via the Scale for assessment of Prodromal Symptoms (SOPS)) in 60 of the CHR individuals at baseline (from 1A), at 6 months, and then 1-year post baseline, testing whether the interaction between proline x COMT activity predicts change in negative symptoms over time. Aim 3. To retrospectively test whether proline x activity predicts CHR conversion to psychosis. Impact: Our study may have implications for negative symptom treatment because proline-modulating medications exist. Modulating proline according to enzyme activity and DA metabolism may hold promise for intervening and targeting negative symptoms in high-risk or RO patients; with important public health implications.